Laser desorption ionization and MALDI time-of-flight mass spectrometry forlow molecular mass polyethylene analysis

Polyethylene's inert nature and difficulty to dissolve in conventional solv ents at room temperature present special problems for sample preparation an d ionization in mass spectrometric analysis. We present a study of ionizati on behavior of several polyethylene samples with molecular masses up to 400 0 Da in laser desorption ionization (LDI) time-of-flight mass spectrometers equipped with a 337 nm laser beam. We demonstrate unequivocally that silve r or copper ion attachment to saturated polyethylene can occur in the gas p hase during the UV LDI process. In LDI spectra of polyethylene with molecul ar masses above similar to 1000 Da, low mass ions corresponding to metal-al kene structures are observed in addition to the principal distribution. By interrogating a well-characterized polyethylene sample and a long chain alk ane, C94H190, these low mass ions are determined to be the fragmentation pr oducts of the intact metal-polyethylene adduct ions. It is further illustra ted that fragmentation can be reduced by adding matrix molecules to the sam ple preparation. (C) 2001 American Society for Mass Spectrometry.